Tuning sulfonic ligand ratio in mixed-linker UiO-66 to modulate Brønsted-Lewis acid synergy for esterification

The present study reports the synthesis of polyol esters from trimethylolpropane (TMP) and fatty acids via an esterification process catalyzed by a series of mixed-linker sulfonic acid-functionalized UiO-66 catalysts with varying sulfonic ligand ratios. A comprehensive structural analysis revealed the successful attachment of sulfonic acid groups (–SO 3 H) to the UiO-66 framework while preserving its characteristic topology. An increase in sulfonic ligand content progressively enhanced the total acidity from 1.67 to 3.71 mmol g −1 , but resulted in a decline in crystallinity and surface area. The UiO-66 containing 40 mol% of the sulfonic acid-containing benzenedicarboxylate linker exhibited the highest catalytic activity. This optimal performance was attributed to the best balance achieved between Brønsted acid site density and Lewis acid site accessibility at this intermediate ligand ratio, enabling effective Brønsted-Lewis acid synergy under pore-diffusion conditions. Furthermore, the catalyst demonstrated excellent reusability over multiple cycles. The present work elucidates the influence of sulfonic ligand ratio on the structure and catalytic performance of UiO-66, providing a robust heterogeneous catalyst for the green synthesis of polyol esters.